1. Field of the Invention
The present invention relates to an automatic focusing device for a camera and a method of controlling the same, and more particularly to an automatic focusing device for an electronic single lens reflex camera with an interchangeable lens, which is provided with an automatic focusing means of a phase difference detecting type and an automatic focusing means of a contrast detecting type, and a method of controlling the same.
2. Description of the Related Art
Conventionally, as an automatic focusing device for electronic single lens reflex cameras with an interchangeable lens, an automatic focusing device of the phase difference detecting type has been widely used. The automatic focusing device of this type carries out focusing of a lens for focusing a taking lens by a defocus detecting mechanism, which is provided in the main body of the camera to perform automatic focusing adjustment, as well as motors provided inside the lens or the camera.
Also, an automatic focusing device of a contrast detecting type which detects a contrast according to high-frequency components of a signal from an image pickup device, and an automatic focusing device which is a combination of the automatic focusing device of the phase difference detecting type and the automatic focusing device of the contrast detecting type have been proposed.
The automatic focusing device of the phase difference detecting type is capable of finding a defocusing direction and a defocusing amount by detecting a focus only once, and hence only a short period of time is required for automatic focusing, and a release time lag is short, which is an important factor for the electronic single lens reflex camera with an interchangeable lens.
On the other hand, the automatic focusing device of the contrast detecting type has the advantage that a high focusing accuracy can be ensured by detecting a focus according to a signal from the image pickup device itself.
However, the automatic focusing device of the phase difference detecting type is constructed such that a focus detecting sensor is provided independently of the image pickup device, which may cause a difference between a focus detected by the focus detecting sensor and a focus detected by the image pickup device due to manufacturing errors, environmental change, secular change, etc. of parts including interchangeable lenses. To ensure a high focusing accuracy which is of great importance to the electronic single lens reflex camera with an interchangeable lens, the camera needs to be large-sized and a very high cost is required. The automatic focusing device of the contrast detecting type has the problem that the release time lag is long since a focus is found by repeating a cycle in which the focus adjusting lens and other parts are moved to detect a focus.
In the case where an automatic focusing device which is a combination of the automatic focusing device of the phase difference detecting type and the automatic focusing device of the contrast detecting type is used, an error caused by manufacturing errors, environmental change, aging change, or the like of parts including interchangeable lenses can be corrected after the focus adjusting lens is quickly moved to a point in the vicinity of a focus, but the number of frames which can be taken per second in sequential shooting (hereinafter referred to as xe2x80x9cthe number of frames to be taken in sequential shootingxe2x80x9d) cannot be increased since two-stage automatic focusing adjustment is required.
It is an object of the present invention to provide an automatic focusing device for a camera, which can increase the number of frames to be taken in sequential shooting while ensuring a high focusing accuracy.
To attain the above object, in a first aspect of the present invention, there is provided an automatic focusing device for a camera, comprising a first focusing unit that carries out a first focusing operation, a second focusing unit that carries out a second focusing operation after the first focusing unit executes the first focusing operation, a storage device that stores a difference between a result of the first focusing operation carried out by the first focusing unit and a result of the second focusing operation carried out by the second focusing unit, and a controller operable in sequential shooting, for providing control to cause the first focusing unit to correct the result of the first focusing operation according to the difference stored in said storage device, and to inhibit the second focusing unit from carrying out the second focusing operation.
According to the first aspect of the present invention, a difference between the result of the first focusing operation carried out by the first focusing unit and the result of the second focusing operation carried out by the second focusing unit is stored, and in sequential shooting, the result of the first focusing operation carried out by the first focusing unit is corrected according to the stored difference while the second focusing unit is inhibited from carrying out the second focusing operation. As a result, it is possible to increase the number of frames to be taken in sequential shooting while ensuring a high focusing accuracy for the second and subsequent frames.
Preferably, the first focusing unit is a phase difference detecting type, and the second focusing unit is a contrast detecting type.
To attain the above object, in a second aspect of the present invention, there is provided a method of controlling an automatic focusing device for a camera, including a first focusing unit that carries out a first focusing operation, and a second focusing unit that carries out a second focusing operation after the first focusing unit carries out the first focusing operation, comprising a storage step of storing a difference between a result of the first focusing operation carried out by the first focusing unit and a result of the second focusing operation carried out by the second focusing unit, and a control step of providing control in sequential shooting to cause the first focusing unit to correct the result of the first focusing operation according to the difference stored in the storage step, and to inhibit the second focusing unit from carrying out the second focusing operation.
According to the second aspect of the present invention, the same effects as in the first aspect can be obtained.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.